The present invention relates to a volume compensation device for hot water heater including a water tank equipped with a cold water inlet and a hot water outlet, in which tank the water to be heated can be heated and stored.
Low pressure or open hot water heaters, as for example hot water storage devices, are constantly in communication with the atmosphere by way of an overflow pipe. The overflow pipe must never be closed because it must always be possible for water which expands when the contents of the water tank are heated to escape through the overflow pipe. The quantity of discharged overflow or expansion water is a function of the increase in temperature and the volume in the water tank. In most cases, the expansion water is discharged through the overflow pipe or through the tap or discharge faucet of a mixing arrangement suitable for low pressure devices.
This drop-by-drop discharge of expansion water results in calcium deposits at the discharge opening of the consumer tap and at the opening of the overflow pipe. On the one hand, such continuous dripping may annoy the consumer while, on the other hand, such calcium deposits also produce unsightly crust formations at the chrome-plated discharge pipes of the mixing device. Moreover, such deposits also reduce the discharge cross section of the overflow pipe. This may produce dangerous dynamic pressures. Regular and complicated decalcification with acid containing media is thus unavoidable.
German Pat. No. 3,040,450 discloses a hot water heater equipped with a volume compensation device for its water tank in which water can be heated and stored in a tank equipped with a cold water inlet and a hot water outlet. The water tank has an associated temperature responsive regulator with which the volume of the water tank can be changed according to the temperature-specific expansion of the volume of the stored water. This regulator is configured either as a temperature responsive, curvable, bimetal expandable bottom inserted into a wall region of the water tank, or the regulator is an expansion zone provided in an annularly circumferential wall region of the water tank, with the expansion of this zone in a direction axial to the plane of the ring being variable as a function of temperature. Alternatively, the regulator is variable in length as a function of temperature and is clamped in between two mutually facing, elastically deflectable membrane walls of the water tank. Moreover, the regulator may be variable in length as a function of temperature and may be supported at one end at a wall of the vessel and at its other end at a compressible membrane chamber disposed at the opposite wall of the water tank. According to another possibility, the regulator is variable in length as a function of temperature and is clamped in between two oppositely disposed walls of the water tank, with the water tank being provided with an annularly circumferential wall region around its longitudinal axis which is elastically expandable in the direction of the longitudinal axis. The regulator is then either a bimetal expansion rod, a bimetal strip or a hydraulic regulator which includes a cylinder equipped with a chamber containing a liquid which expands when heated and charges a membrane or a piston.
To equip such water tanks with curvable bimetal expansion bottoms or with membrane-like side walls in mass production requires enormously large expenditures for tools. Moreover, the introduction of a curved bimetal strip between two oppositely disposed elastically expandable walls of the water tank is handled, with respect to manufacturing technology, only with great difficulty and involves high installation costs. Since the water tank is subjected to constant mechanical changes in movement, only costly bronze sheet metal can be used as the wall material in such cases. If the otherwise customary thin copper sheets were used as the material for the tank, the water tank would tear open at the points of expansion after a relatively short period of operation because of these alternating mechanical stresses and would thus no longer be tight. The use of inexpensive plastic tanks, which must have relatively thick walls, is also impossible because of their relative rigidity.